/Engine/Source/Runtime/Engine/Classes/Engine/NetSerialization.h
ScaleFactor is multiplied before send and divided by post receive. A higher ScaleFactor means more precision. MaxBitsPerComponent is the maximum number of bits to use per component. This is only a maximum. A header is written (size = Log2 (MaxBitsPerComponent)) to indicate how many bits are actually used.
namespace UE { namespace Net { namespace Private { template<int32 ScaleFactor, int32 MaxBitsPerComponent> bool UE::Net::Private::LegacyReadPackedVector ( FVector3f & Value, [FArchive](API\Runtime\Core\Serialization\FArchive) & Ar ) } } }